Sorry about my cynicism, but that thing looks pretty useless. Why would you drop a swarm of these things on a submarine's (U-Boat's) exact position if you can detect them already? The ambient noise of the machinery within the sub would probably make more noise. It's not very descriptive in this video either. Dose it have a little motor and battery in it? Or does it rely on the current of the water moving around the hull. I think it was one of those things that were tried and failed.
Funny idea though...
